Sludge consists of various elements such as waste, organic and inorganic compounds that are disposed into atmosphere which are harmful to the atmosphere. Sludge contains various pollutants and solid waste such as heavy metals, large organic solids, calcium and magnesium, metal sulphides, heavy metals organic complexes, precipitated soaps and detergents, biomass and precipitated phosphates. The method or treatment of sludge involves stabilization and dewater residue.
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Various types of unit processes and unit operation are used for the management of sewage sludge process which are enlisted below, because of the wide variability in sludge characteristic and difference in acceptability of treated sludge for ultimate disposal is impossible.
Fig.1.1 Municipal Sewage Sludge(MSS)
a. Land filling
c. Open dumping
Fig.(a) Land filling
Fig.(c) Open dumping
Biomass waste are the aggregates obtained from agricultural land such as crop left over, animal fodder, organic industrial, human and animal waste. It is the materials obtained from plants which requires sunlight to flourish.
Biomass are derived from various other general and special purpose sources such as woods from forest, forest leftover, sugarcane bagasse, rice husk, kitchen waste. Biomass waste containing various advantageous materials till now were not taken into use. Until now the waste obtained from above enlisted sources used to get simply dumped into landfill or used to get burned in some open areas creating various pollution issues in the surrounding humiliation.
Energy obtained from biomass is generally due to the carbon dioxide contained in the material which is generally due to the sunlight trapped in these materials and due to the photosynthesis process. If these biomass waste gets leftover for longer period of time it will get break down thereby releasing energy stored and the carbon dioxide contained in the waste. These energies if released in a quick, directed and regulated way can get used in various useful way.
Fig.1.2 Biomass waste
Pyrolysis is a process of chemically decomposing organic materials at elevated temperature in the absence of oxygen. The process typically occurs at temperature above 400o C temperature and under pressure.
Co-pyrolysis is the similar to the pyrolysis process but is carried out using two or more than two materials feed stock.
Fig.1.3 Process setup
PYROLYSIS AND CO-PYROLYSIS
The word pyrolysis is found from the ancient Greek dictionary in which ‘pyro’ meant fire and ‘lysis’ meant separating so directly the word itself states the purpose and meaning of itself. Pyrolysis is a chemical process of decomposition of organic materials at high temperature in absence of oxygen and a controlled condition under pressure. It is commonly used to convert organic materials into solid residue containing as and carbon along with small quantity of oil and gases. Pyrolysis using extreme conditions or extreme pyrolysis yields carbon as product and is also called as carbonization. Pyrolysis carried out using various feed materials contains different amount of yield and the amount of residues also depends upon the initials carbon contents, organic and inorganic material content and heavy metal content of the feed materials. The carbon composition in the char and the oil obtained are in direct proportion to the initial carbon content of the feed/raw materials used in the initials stages. Unlike other processes pyrolysis doesn’t involve reaction with water, other reagents or oxygen.
There are main three types of pyrolytic process depending upon the process time and biomass temperature. Names of these pyrolysis are as below
These process is characterized by length of solids and the gas residence time, low temperature and slow biomass waste heating waste. Here the temperature ranges from 0.1o to 2o C temperature per second and the temperature prevailing to nearly 500o C temperature. The residence time of biomass waste ranges from minutes to certain days while that for gases may be over eight seconds. During slow pyrolysis char and tar are released as the main products as the biomass waste is slowly devolatilized.
It occurs at temperature ranging between 400oC to 600oC and at rapid heating rates. The vapour residence time for the flash pyrolysis process is less than two seconds. The comparative production of char, gas and tar is less than slow pyrolysis.
2.2.3 Fast pyrolysis
Fast pyrolysis process is primarily used to produce bio-oil and gas. During fast pyrolysis the biomass waste is heated to temperature ranging from 650oC to 1000oC. The temperatures are recalculated depending upon the desired amount of bio-oil and gas products. The char is obtained in large quantity as residue and has to be removed frequently.
Co-pyrolysis is a process which involves two or more materials as a feedstock. Many studies have indicated that the use of these process have enabled to improve the characteristics of the oil as it increases the oil yield, reduce the water content and increase the calorific value of oil. Besides the use of these technique it has also reduced the production cost and is also enabled to tackle some waste management and pollution issues that are being created due to the disposal of waste to open areas.
Co-pyrolysis is the process which does not involves solvents, catalysts, additional pressure, waste from process and no complicated equipment. It is the process which saves cost for waste treatment, solves various environmental problems, significantly reduces the waste, enhances energy security and its feedstock is available worldwide.
Fig.2.5 Co-pyrolysis Overview
Recent Trend, suggest that biochar gets immense importance in the field of global environment. Biochar has mainly been used as soil amendment, carbon sequestration and also used as adsorbent for treatment of waste water. Earlier they didn’t find specific way to use of Biochar. Literature suggest that Biochar has a great potential to adsorb environmental contaminants. Biochar is a carbon rich solid product derived by pyrolysis or co-pyrolysis of biomass and MSS with little oxygen or no oxygen. One of the Literature suggest that chars obtained from three different Mixtures. Comparing the data of samples of chars. Which give brief idea about the char adsorption capacity. Literature study are to perform an efficient upgrading biochar. For better production of Biochar or upgrading biochar the sewage sludge has been proved to be a good feedstock. Biochar as an adsorbent has many applications like removing heavy metal ions from waste water and also treatment of dye waste water. Production of Biochar also have many advantages like management of Municipal Sewage Sludge. There are many literatures are available to characterize the biochar. They are mainly Characterize the physical and chemical properties. They had been using the different parameters. The biochar were crushed to and sieved into various ranges. Another characterize parameter is CHNOS elemental analyser. This test give which elements contain in Biochar.
Thermo gravimetric analysis of Biochar was performed with an integrated thermal gravimetric analyser. One of the well-known literature suggest that Sewage sludge has been proved to be a good feedstock material for the production of Biochars. They are using the biomasses like Rice Straw(RS) and Sawdust(SD) However, the problem is that the total/leachable contents of some heavy metal elements in biochar exceed the corresponding norms. In this work, efforts were made to solve above the mentioned topic through the addition of other Biomasses (rice straw(RS)) and sawdust(SD) for the co-pyrolysis with SS. The addition of RS/SD reduced the yield of biochar, while contents of organic matter in biochar were significantly improved. Thermal stability, surface area and pore volume of biochar depend upon the 2 factors addition of biomasses and especially the addition of SD. The total contents of heavy metals in biochar products, especially their Cu, Zn, and Ni contents, were reduced. Reduction of the mobility of heavy metals in biochar according to the toxicity characteristic leaching procedure was not observed. The sewage sludge has some characteristics, namely high moisture content, ash, high density and viscosity, low heat value. Crop straw contains lower ash, and it can be made into high heat value pyrolysis products.
The potential of residue biochar derived from co-pyrolysis of dewatered sewage sludge (80% of moisture content) and pine sawdust for the adsorption of methylene blue (MB) from aqueous solution was studied. The biochar was characterized by scanning electron microscope, X-ray fluorescence, Brunner-Emmet –Teller (BET). Adsorption experiments were carried out to investigate effects of various parameters on MB adsorption and evaluate the surface area and maximum adsorption capacity for MB. The adsorption process was followed the second order kinetic equation, suggesting that the adsorption might be a chemisorption process. The experimental adsorption isotherm data were well fitted with both Langmuir model and Freundlich model. Adsorption experiments were performed in batch mode to evaluate the effects of various parameters on adsorption of MB. In each experiment 100 ml of dye solution with 1 g/L of adsorbent was added in a 250 ml conical flask. The sample was shaken at 190 rpm for 240 min. other literature survey give brief idea about Products yield and Biochar Characteristics. As we know from pyrolysis we get 3 products, Biochar, Bio-oil and syngas. Bio-oil and Biochar yields were calculated on a wet biomass basis, and the non-condensable gas yield was calculated by the difference and the liquid organic yield was calculated by subtracting the water content from bio-oil yield.one of the literature give idea about the Proximate analysis, pH and Cation Exchange Capacity. The contents of Volatile matter and ash determined using the American Society Testing and Materials. Volatile content was determined as weight loss after heating the char in a covered crucible to 950°C and holding for 7 min. Ash content was determined as weight loss after combustion at 750°C for 6 h with no ceramic cap. The pH of biochars was measured using a pH meter at 1:5 solid /water ratio after shaking for 30 min. Then next parameter is Surface properties of Biochar. The surface morphology of these biochars was examined using scanning electron microscope. SEM micrographs of biochars produced at different temperatures. Image shows that the Biomass had softened, melted and fused into a mass of vesicles. The Vesicles were the result of volatile gases released within biomass. As temperature increased, more volatile gases released from the biomass. For getting the adsorption data we have to using Brunauer-Emmett-Teller (BET) surface area and Langmuir adsorption isotherm.
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